If you're just joining us for the Final Fantasy action, be sure to check out the previous articles going over the White and Blue cards
Whenever Eternal Scourge becomes the target of an Instant or Sorcery spell, it's exiled from play - but, its controller can cast it from exile to the battlefield
Common Errors: A Primer There was an error retrieving a chart for Trial // Error For an excellent beginner's guide, I can do no better than recommend MisprintedMTG
The point of all of this is to teach you a few key lessons
They run a large number of cantrip spells like Ponder and Brainstorm, plenty of ritual effects like Dark Ritual or Pyretic Ritual, and usually some recursion effects to make casting upwards of 10 to 15 spells in a single turn viable, like Past in Flames, one of the strongest flashback effects in Magic
In fact, it works best in the early game as most players are casting cheap Artifacts like Sol Ring and may not be able to pay the extra 1 Mana to prevent you from drawing a card